Parametric amplifier using conducting magnetic member



Jan. 18, 1966 D, s. RODBELL PARAMETRIC AMPLIFIER USING CONDUCTINGMAGNETIC MEMBER 2 Sheets-Sheet 1 Filed July 26, 1965 UNIFORM MODE 1 7)ve n for: Dona/d 8. R be/ 5 222'o 5% 1966 D. s. RODBELL 3,230,463

PARAMETRIC AMPLIFIER USING CONDUCTING MAGNETIC MEMBER Filed July 26,1965 2 Sheets-Sheet 2 l L r q I q J 200 400 600 800 rewet'mr/amaz &

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United States Patent 3,230,463 PARAMETRIC AMPLIFIER USING CONDUCTINGMAGNETIC MEMBER Donald S. Rodbell, Burnt Hills, N.Y., assignor toGeneral Electric Company, a corporation of New York Filed July 26, 1965,Ser. No. 474,826 Claims. (Cl. 330-43) This application is acontinuation-in-part of my application Serial No. 65,085, filed October26, 1960, and now abandoned, entitled Magnetic Microwave Device andassigned to the assignee of the present invention. The present inventionrelates to devices employing magnetic resonance and particularly to suchdevices as require large microwave magnetic field strengths.

A number of magnetic materials are known to display a magnetic spinresonance when magnetic energy is Thus, a magnetized body will displayan absorption of an applied radio frequency pump signal. As thefrequency of the applied signal is varied a certain resonant frequencymay be achieved at which RF, power absorption is maximum. Bodies of suchmagnetic materials also exhibit conditions of saturation ornear-saturation for an applied magnetic field where distinctlynon-linear changes occur in the susceptibility of the material aftercertain levels of pumping power are applied at the resonant frequency.Therefore magnetically resonant elements are useful components oflimiters, mixers, frequency converters and the like at the radiofrequencies corresponding to resonance.

In one instance a parametric amplifier is possible including a magneticbody having considerable power applied at the pump frequencycorresponding to the frequency of magnetic resonance. An R.F. inputsignal, also suitably applied to the magnetic body, can be made to mixwith the pump signal and furthermore be amplified. -An additionalresonance is provided at an idling or difference frequency either by themagnetic element or associated apparatus.

Quite large R.F. magnetic field strengths are often required to producethese effects and hence these devices are conventionally regarded ashigh power devices wherein a small volume of magnetic material isdisposed in a strong R.F. magnetic field established in a cavityresonator. Pump signals as large as kilowatts peak power are typical atthe microwave frequencies these magnetic devices prove most useful; suchpowers are not only expensive but in many cases diflicult or impossibleto generate, especially at frequencies above 10 kilomegacycles/ second.In some instances pulsed magnetron equipment has been employed toproduce such powers and then only for intermittent periods.

In accordance with a feature of the present invention a magneticallyresonant element comprising a combination conducting and magneticelongated body is oriented at a point of high electric field in anamplifier or mixer, whereby the body concentrates the energy of theincident electromagnetic wave to produce strong R.'F. magnetic fieldeffects in the body. A greatly improved coupling between incident energyat the frequency of magnetic resonance and the resonant magneticmaterial is produced compared with the energy coupling attained byplacing a solely magnetic body at a point of high magnetic field. Powerrequirement reductions of several orders of magnitude are achieved.

3,230,463 Patented Jan. 18, 1966 "ice According to another feature ofthe present invention the elongated filamentary element comprises aferromagnetic monoc-rystalline iron whisker.

The subject matter which I regard as my invention is particularlypointed out and distinctly claimed in the concluding portion of thisspecification. The invention, however, both as to organization andmethod of operation, together with further objects and advantagesthereof, may best be understood by reference to the followingdescription taken in connection with the accompanying drawings whereinlike reference characters refer to like elements and in which:

FIG. 1 illustrates magnetic spin resonance in a magnetized body;

FIG. 2 is a phantom view of a device illustrating the operatingprinciples of the present invention;

FIG. 2a is a cutaway view of another device illustrating the operatingprinciples of the invention;

FIG. 3 is an illustration of spin waves in a magnetic body;

FIG. 4 is a graph of frequency vs. wave number for the normal modes of amagnetic material;

FIG. 5 is an idealized plot of the magneto crystalline anisotropy fieldfor iron vs. temperature;

FIGS. 6 and 7 are respectively isometric and cross-sectional views of afrequency multiplier according to the present invention;

FIG. 8 is a perspective view of a parametric amplifier according to thepresent invention;

FIG. 9 is a schematic illustration of charge excursion in the elongatedconducting element according to the present invention; and

FIG. 10 is a plot of field vs. temperature for an iron whiskerembodiment according to the present invention.

The theory and phenomena utilized by the present invention will beexplained with reference to FIG. 1 depicting unpaired electrons 1 and 2in a body of magnetic material disposed between a static externalmagnetic field represented by north pole 3 and south pole 4. Theelectrons spin with angular velocities around their own axis so that theelectrons may be thought of as tiny magnetic dipoles or magnetsproducing a magnetic moment along their spin axis. In the event of amagnetic crystalline material disposed in the external magnetic field,the magnetic moments become aligned between the external poles. If anoutside force or source of energy is now applied to the magneticmaterial, the magnetic moments will tend to precess or oscillate aboutthe original axis (between the external magnetic poles 3 and 4), theirmagnetic moments 5 describing a path thereabout as at 6. This precessionmotion is distinct from the electron spin motion. The precession willtend to occur at and define the resonant frequency of uniform precessionfor the magnetic material, and if the additional forces should be in theform of an applied oscillating magnetic field 7 such a field willproduce a greatly increased precession angle if the magnetic energy alsooscillates at the resonant frequency of the uniform precession.

If the body of magnetically resonant material is disposed at a point ofmaximum magnetic field in an RF. resonant cavity with RF. energy at thecavitys frequency applied thereto, and if the cavitys frequency is theresonant frequency of the magnetic material then, theoretically, a largeprecessional angle will occur in the material. Non-linear operation andpossible coupling will then result for an optimum precession angle andis attributable to the resonant non-linear component of magnetization inthe direction of the static field caused by the precession. Therefore,if two R.F. magnetic fields are applied to the magnetic material in FIG.1, both perpendicular to the static field produced by poles 3 and 4, sumand difference field components will occur in the direction of thestatic field, if at least one of the incident fields produces asufiicient precession angle 5) to result in the non-linear couplingoperation.

Operation is preferably had at a precession angle near or approaching asaturation condition for the material.

Heretofore if a magnetically resonant material was employed as anon-linear electronic device, such magnetic element was often placed inan R.F. resonant cavity at a maximum magnetic field point in order toenjoy the strongest magnetic field strength available for a givenincident R.F. power and thereby attain a maximum precession angle in themagnetic material. The material conventionally used was a magneticceramic body, for example, ferrite, and was non-conducting to allowmaximum permeation of a magnetic field into the element.

However, in accordance with the present invention the magneticallyresonant element has conducting properties as Well as magneticproperties and furthermore, is disposed at a point of maximum electricfield and generally parallel thereto rather than being disposed at apoint of maximum R.F. magnetic field. The element is also preferablylonger in the direction of the RF. electric field than in the directionof the RF. magnetic field and preferably of very small transversedimension as depicted at 8 in FIG. 2, wherein a phantom view of a deviceillustrating the operating principles of the present invention isrepresented.

Referring to FIG. 2, the elongated filamentary element 8 according tothe present invention is disposed in a space resonant device which maycomprise a cavity 9 having a coupling iris 10 for introduction ofelectromagnetic radiation at the resonant frequency of the cavity. Thiselectromagnetic radiation is also at a magnetically resonant frequencyof filamentary body 8. The cavity 9 may be arranged to support the TEmode such that the distribution of electric field is depicted by a sinewave 11 having a maximum electric field point at 12 and with which thefilamentary body is vertically aligned. That is 'to say, the filamentarybody is preferably disposed vertically and wavelength from end wall 13of the cavity while being half way between the narrow vertical sidewalls of the cavity. The body may be supported in the cavity by anysuitable insulating means, for example, a quartz tube (not shown). Astatic D.C. magnetic field is provided in a chosen direction withrespect to the filamentary body 8, for example, by means of DC. magnet14 energized by an operating coil 15. The field is selected to producemagnetic resonance at the operating frequency and for the desired mode.

An alternative configuration is illustrated in FIG. wherein theelongated element 8 is disposed along the electric field in a re-entrantcavity 9a. The electric field is quite strong in the center of this typeof cavity. It is, of course, understood that other cavity configurationsmay be employed.

The elongated filamentary element 8 may be formed of suitable materialswhich are conducting and which exhibit magnetic resonance. The materialshould exhibit high permeability as well as reasonably low resistivity.One preferred form of such element is an elongated iron whisker being asingle crystal of iron. Such material has the advantage of having arelatively narrow absorption line width and therefore is veryadvantageous in providing near-saturation conditions at relatively lowincident pumping powers, in accordance with the formula:

where H is the incident radio frequency field required for saturationonset, AH is the absorption line width and M is the characteristicsaturation magnetization of the body.

In addition, certain other materials may be suitably employed. Forexample, the elongated element may comprise a long thin wire formed ofan alloy of about nickel and about 20% iron frequently referred to asPermalloy. Another exemplary material from which such a wire may beformed is a copper-cobalt alloy in which the cobalt content approximates2% and is distributed as precipitate particles through a copper matrix.

Such an elongated body according to the present invention is alsogeneric to a conducting wire having a magnetic coating or magnetic bodydisposed therearound.

With the elongated filamentary element according to the presentinvention it has been found possible to produce a given R.F. magneticfield strength with less than the incident power heretofore employed forbringing about non-linear magnetic resonant conditions of a magneticbody disposed in an R.F. resonant cavity. This enhanced field producedin and by the elongated element of the present invention is furtherconsidered in connection with FIG. 9 where the elongated body is takenfor convenience as a long thin cylinder having a length L, and thedistance from the left hand end of which is designated as the variablex. In performing calculations of resultant magnetic field we first askhow much charge must one place on the ends of the body so that theapplied electric field will be cancelled out along the surface of thebody as it must be if the body is conducting. For convenience the centerof the body is taken as a point where the field is cancelled. Then:

E(;; is the voltage of point x, e is the dielectric constant of freespace, and q is the charge taken to exist at each end of the body,

The current due to the reversal of this charge excursion will be behindq and E in time phase but in magnitude will be:

where r is the radius of the body and j is the frequency. of the appliedsignal. Taking w as 21rf, the field The ratio of this created field tothe maximum magnetic field that would otherwise exist in the cavity thenapproximately equals:

where Z0 is the ratio of maximum electric to maximum magnetic field.

i Employing rationalized MKS units,

10 couloumbs 361 volt meter and typically the ratio of maximum electricto magnetic field Z=377 ohms Then for an X-band frequency of 10megacycles=10 cycles per second,

H nr.

This calculation should be taken as approximate.

Further, the incident power required for establishment of a given R.F.field is proportional to the square of the field. Therefore, the ratioof the power required to establish a given maximum field by means of theelongated element of the present invention, to the power required in themagnetic body as used heretofore, equals the square of the ratio of thefields produced by the two methods. Therefore the power required toproduce a given RF. magnetic field strength by means of the elongatedelement divided into that existent for a typical prior art mag- It isnoted that the field ratio is proportional to the square of the bodylength divided by its radius and since the power ratio is proportionalto the square of the field ratio, this means that the power advantagegained is proportional to the 4th power of the elements length. It isthen desirable to form the elongated filamentary element as long andthin as possible. A ratio of at least 10 to l of length over transversedimension is preferred.

For a further exposition together with experimental findings regardingthe above described effects, reference is made to the article TheMicrowave Magnetic Field Near a Conducting Perturbation by Donald S.Rodbell, Journal of Applied Physics, November, 1959.

The illustrative apparatus depicted in FIG. 2 (or FIG. 2a) may beemployed with suitable additions as a mixing or amplifying deviceaccording to the present invention. For example, if the space resonantdevice of cavity 9 is rendered additionally resonant by means (notshown) at additional selected frequencies, the apparatus can be used asa parametric amplifier or as a mixer. For parametric amplification totake place three principal high frequency components are conventionallyinvolved, i.e., a pump frequency f the signal frequency f,,, and anidler frequency f, equal to f In the parametric amplifier the signalfrequency is modulated or mixed with the pump frequency to produce theidler frequency. In turn, the idler frequency mixes with the pumpfrequency to produce the signal frequency again. If phase relationshipsare correct in the systems feedback, the signal current can be built up.Amplification is therefore obtained, or if the signal output is unloadedthe system will oscillate.

In order to sustain such parametric amplification resonant circuits ormeshes are provided at both the signal and idler frequencies while meansare also provided for modulating both the signal frequency and idlerfrequency with the pump frequency.

In the FIG. 2 apparatus the elongated element 8 is driven into thenon-linear resonance by the incident pump signal 11, admitted throughiris 10. If the resonant cavity 9 is additionally resonant at thefrequency of a signal f (also admitted into the cavity) and at thefrequency of a suitable idler frequency at f parametric amplificationcan result wherein a signal frequency of increased amplitude isretrieved or reflected from the cavity, and with the greatly decreasedpumping power requirements as aforesaid, the pump signal driving theelement 8 into a nonlinear region in order to provide the mixingfunction.

The pump and signal frequencies may be admitted through iris 10.Alternatively, the element 8 may be extended through an apertureprovided in the cavity with one or more high frequency currentsexternally excited therein.

Although thoroughly possible, it is sometimes difficult to render asingle cavity resonant at a number of frequencies each with desired Q.It is therefore frequently convenient to employ an element 8 whichitself is responsive at one or more frequencies. One usual principalresonant frequency associated with a magnetically resonant element isthe frequency of uniform precession conventionally referred to as theuniform mode. When a magnetic resonant element is operating completelyin the aforementioned uniform mode, all of its spinning electrons may bethought of as precessing as shown by the precessional angle in FIG. 1,this being one state of such a system. However, the system may alsosustain a spin wave phenomena between electrons in the crystal latticeof the magnetic body as illustrated in FIG. 3.

In FIG. 3 the various electrons continue to precess but their magneticmoments may be oriented at different angles with regard to one anotherthroughout the crystal. These disorientations may be described asregular patterns throughout the crystal and are the so-called spinwaves. If the system is non-linear, energy may be exchanged between spinwaves and the principal or unifonn mode. One spin waves wave-fronts areillustrated by diagonal lines in FIG. 3 and the wavelength A isindicated between two such wave fronts with the spin wave propagationdirection being given by the long arrow. The frequencies of spin waveswhich may exist in the magnetic sample are not proportional to thewavelength A but take on a distribution as illustrated in FIG. 4, wherethe frequency is plotted against their individual wave number k equal to21r/x, for a long, thin magnetic element. If the magnetic element willsupport appropriate spin waves as well as or instead of the uniformmode, one or more spin waves may be substituted for resonant frequenciesof cavity 9 in the FIG. 2 apparatus. Spin Waves may also be driven byelectromagnetic energy additionally provided to the cavity at spin wavefrequencies. Thus the cavity 9 may be resonant at the pump frequencyalone, depicted by wave 11, this frequency also being a frequency ofprecession in element 8, and wherein spin waves in element 8 arerespectively employed at f and 7, for supporting parametricamplification. In like manner a principal precession and one spin waveor two spin waves may be employed in the element 8 with only oneadditional resonant frequency being provided by the cavity.

Certain spin waves having low wave numbers are frequently spoken of asdefining magnetostatic modes and the operation employing these modesspoken of as magnetostatic and semi-static operation.

It is understood that the various schemes applicable to parametricamplification are similarly applicable to the simpler case of afrequency mixer or converter.

The operating frequency of the principal precession called the uniformmode in a magnetic resonant element is given by the formula where H isthe applied external field (and in addition any crystalline anisotropy);'y is the magneto mechanical ratio; M is the characteristic saturationmagnetization; and N N and N are demagnetization factors related to theshape of the magnetic element (for a generally ellipsoidal body). Thisformula is applicable to the uniform precession when employed as theprincipal resonant mode in the elongated element according to thepresent invention. With the present invention more frequent use is madeof the electric or curl mode for the principal non-linearly driven modeas herein described. In the curl mode case, the demagnetization factorsin the formula are those appropriate to a flat plate, i.e.

The frequency of usable spin waves in the element is given by thefollowing formula:

The longer wave length spin waves are more affected by the shape of themagnetic element. For expressions of frequency for the magnetostaticmodes, as well as the uniform mode, reference is made to R. L. Walker,Physical Review, vol. 105, (1957), page 390.

The frequency of principal curl mode precession in the conducting andmagnetic elongated filamentary body according to the present invention,e.g., wherein the body is homogeneously conducting and magneticthroughout so that current and magnetic field are in effect limited toan outer skin depth of the elongated body, is given as previously statedby the following expression:

where H is the applied static magnetic field, and

H is a function of the material and is the magneto crystallineanisotropy field. For iron H is relatively large but depends upon theoperating temperature. At room temperature the operating frequencyaccording to the above formula, when applied to an iron whisker asdescribed, is greater than 9 kilomegacycles and therefore if operationis desired in the X band or below, the apparatus employing the magneticelement should be desirably operated above room temperature. A relationbetween H and temperature for an iron whisker is plotted in FIG. 5. Itshould be noted that at higher frequencies this temperature of operationis substantially lowered.

The terminology curl mode comes from the Maxwell relation,

Curl F=7+ at where I is current density and BE/Et at the time rate ofchange of the electric field. This is a statement of the field producedaround a conductor and the mathematical description curl is the originof our nomenclature. That is to say, the charge flow or excursion in theconducting portion of the elongated element of the present inventionproduces a circular magnetic field therearound which is symmetricalaround the axis of the element rather than being uniform.

In FIG. 10, plots a and b represent respectively applied D.C. field vs.temperature for the curl mode and the uniform mode in an iron whisker,the frequency of the applied signal being held constant at an angularfrequency which shall be designated w The frequency of 0.1 in thepa'rticular test from which the curves a and b were drawn was 9kilomegacycles. Curves c and d are plots of DC. field vs. temperaturefor the curl mode and uniform mode in an iron whisker for a somewhathigher frequency, 0: It may be readily appreciated that ta can beadjusted so that the uniform mode, d, for 01 will cross the curl mode,a, for w at a crossover point 0. That is, modes d and a are degenerateat this point and if one of them, preferably the curl mode a, is drivento nonlinear operation, energy coupled into one mode will find its wayinto another in the same manner that energy coupled into the uniformmode or curl mode may find its way into the spin wave modes or viceversa.

In this manner both the curl and uniform modes in a single conductingmagnetic element may be utilized to transfer energy from one frequencyto another. A device employing this type of operation is illustrated inFIGURES 6 and 7 wherein the elongated conducting and magnetic element 17extends through an aperture between a first waveguide or cavity 18operating at m and a second waveguide or cavity 19 operating at m Bothwaveguides preferably operate in the TE mode so that the elongatedelement 17 is disposed along the electric field of each guide or cavityand is preferably spaced a quarter of a wavelength from the shorted endof each guide or cavity so as to be at a point of maximum R.F. electricfield in each. Electromagnetic energy in the guide or cavity 18 exciteselement 17 in its curl mode at m The energy supplied waveguide or cavity18 should be sufficient to drive element 17 to non-linearity. Thissituation allows the communication of energy to other possible modes; inparticular mode at of FIG. 10 can be realized and the energy employedvia guide 19. Other embodiments for employing both curl and uniformmodes :are readily suggested such as parametric amplifying devices,mixes, and the like, as hereinbefore disclosed. A principal feature isthat at a low power expenditure at a frequency m one can obtain usefulpower at a frequency m A cascaded system of these devices can be used togenerate higher and higher frequencies by the frequency step-upconversion.

FIG. 8 illustrates a parametric amplifier configuration according to thepresent invention employing electromagnetic operation. Two frequencies,the signal frequency 1",, and the pump frequency f are applied throughrectangular waveguide 20 to a bimodal cruciform cavity 21. A roundcoupling iris 22 located centrally with respect to both the bimodalcavity and the waveguide allows entrance of energy at both frequenciesto the cavity. The cruciform bimodal cavity 21 is composed of a firstrectangular section 23 resonant at the signal frequency f, and a secondrectangular section 24 perpendicular to the first, resonant at the pumpfrequency. Both sections 23 and 24 are oriented at an angle ofapproximately 45 with regard to the long wall of waveguide 20 and thesesections 23 and 24 also have a common central area for central placementof iris 22 and also for housing a capillary tube 25 containing elongatedconducting and magnetic element 26. The capillary tube 25 is alsooriented at an angle of approximately 45 with respect to cavity sections23 and 24 but is substantially perpendicular to the long wall ofwaveguide 20. The capillary tube is placed approximately one quarterwavelength (at the pump frequency, f from the end wall opposite thecoupling iris 22 and extends from one cruciform juncture diagonallyacross the central area of the cavity and out through a small aperturein the diagonally opposite cruciform juncture. Magnetic element 26,which has conducting and magnetic properties, extends from within thebimodal cavity out through the small aperture which receives thesurrounding capillary tube 25 and is there encircled by a single turncoil 27 connected by means of leads 28 to a resonant circuit 29 tuned toan appropriate idler frequency, f,. As before, the various frequenciesare arranged such that f =f +f The two resonant frequencies of cavitysections 23 and 24, that is, f and f respectively, are kept separateinsofar as the ends of these sections are concerned in conjunction withwaveguide dimensions by means of a quartz mode separator 30 placed inone end of section 24.

The tuned circuit 29 may be any convenient resonant circuit tuned toan'appropriate f and, for example, may actually comprise abutterfly-type tank circuit useful up to about 1,000 megacycles asdescribed in the third edition of Radio Engineering by F. E. Terrnan, atpage 434. Alternatively, this resonant circuit 29 may comprise anadditional resonant cavity abutting the walls of cavity sections 23 and24 having magnetic element 26 extending therein through a small aperturefor receiving capillary tube 25. The alternative idler cavity will bemore appropriate, of course, for higher idler frequencies. A staticmagnetic field longitudinal to magnetic element 26 is brought about bymagnetic north pole 31 and south pole 32 disposed at either end of thecapillary tube. The field thereof is appropriate to establish aprincipal resonant mode in element 26 at f In operation the apparatus ofFIG. 8 functions to amplify the signal frequency 1; introduced intocavity 21 through waveguide in that an incident frequency signal isreflected out of the cavity in amplified form. The presented incidentsignal frequency initially establishes a standing wave pattern in cavitysection 23 such that an electric field maximum is presented at rnagneticelement 26. The pump signal frequency f also presented through waveguide20 excites cavity section 24 to resonance so that an electric fieldmaximum of the pump signal is also presented at magnetic element 26. Thepump signal, of course, is a local signal of much higher power and israised to a level suificient for driving element 26 into a non-linearregion of operation near saturation. This is accomplished by the veryenhanced magnetic field existing in element 26 in the principal or curlmode caused by electric field excitation thereof produced by electriccharge excursions in the element. Further, since the element isoperating non-linearly, the signal frequency electric field maximum alsoincident upon the element will couple and mix with the pump modetherein. It is noted that the signal frequency as well as the pumpfrequency both cause precession in the element 26 inasmuch as bothfrequencies result in magnetic field components which may be taken asperpendicular to the static magnetic field, in accordance with thearrangement of element 26 in the capillary tube whereby the element 26is diagonally oriented to receive components of perpendicular excitationfrom both cavity portions 23 and 24. That is to say, element 26 has acomponent of its length parallel to each electric field (in cavitysections 23 and 24) and therefore both electric fields can causeprecession in the element 26. The power of the pump frequency ispreferably strong enough to cause a relatively large angle of precessionand therefore due to the nonlinearity of the resultant magnetic fieldalong the length of the element 26, a difference-frequency magneticmoment is built up along the length of element 26, equal in frequency tof the idler frequency. Energy is coupled at the idler frequency to tunedcircuit 29, which is tuned to the idler frequency. Energy is built up inthe idler mode by means of tuned circuit 29 which, in turn, causes alongitudinally directed magnetic field in element 26 at idler frequency.This idler magnetic field in turn frequency modulates the magneticprecession in the element 26 mixes with the pump frequency f producingan amplified output at the signal frequency f In this manner, energy istransferred from the pump source at the frequency f to the signalfrequency f This signal is amplified and is re-delivered to wave guide20 through aperture 22.

When a material is spoken of in this application as being magnetic, amaterial is meant which has a permeability substantially greater thanone.

Similarly, a conducting material is taken to mean one having aresistivity substantially less than 10,000 micro ohm centimeters.

While I have shown and described several embodiments of my invention, itwill be apparent to those skilled in the art that many other changes andmodifications may be made without :deparing from my invention in itsbroader aspects; and I therefore intend the appended claims to cover allsuch changes and modifications as fall within the true spirit and scopeof my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A parametric amplifier comprising a hollow cruciform bimodal cavityhaving two mode portions supporting electromagnetic field distributionsin orthogonal direction-s and provided with an aperture adjacent bothsaid mode portions, an elongated member supporting electric conductionand for supporting a magnetic field which member exhibits non-linearmagnetization, said member being angularly disposed in the centralportion of said bimodal cavity with a major component of its length in adirection substantially parallel to electric field maxima in theelectric field maxima in the central portion of said cavity andextending through said aperture, one mode of said cavity being resonantat an amplifier input frequency and another mode being resonant at apurnp frequency, a second resonant system coupled to the extension ofsaid member, and a D.-C. magnetic field acting upon said member forproducing gyromagnetic resonance in said member so that said membermagnetically resonates at the pump frequency of said cavity, said secondresonant system resonating at an idler frequency whereby to provideparametric amplification in said cavity.

2. A parametric amplifier comprising a resonant waveguide cavity, inputmeans coupling signal radio frequency energy to said cavity and pumpradio frequency energy to said cavity to produce in said cavity anelecrtomagnetic field distribution corresponding to each of saidenergies including electric field maxima and minima, said cavity beingprincipally resonant at the frequency of at least one of said energies,an elongated member for supporting electric conduction and forsupporting a magnetic field therealong which member exhibits non-iinearmagnetization disposed at a location of high electric fieldconcentration in said cavity having at least a major component of itslength aligned with the electric field distribution to provide anenhanced radio frequency magnetic field in said cavity and member, D.C.magnetization apparatus producing a static magnetic field in said memberfor establishing gyromagnetic resonance therein at the frequency of saidpump energy, said pump energy being provided at a power level sufiicientto establish a large precessional angle in said member as a result ofsaid enhanced radio frequency magnetic field, wherein precession aroundthe transverse circumference of said member is substantially axiallysymmetric, and another resonance system coupled to said member forproducing a magnetic field having a component axial to said member at afrequency equal to the difference between the frequency of said pumpenergy and the frequency of said sign l energy whereby to provideamplification in said cavity at the frequency of said signal energy.

3. The amplifier according to claim 2 wherein said member is filamentformed of electrically conductive and magnetic material, said filamenthaving a length at least ten times its transverse dimension.

4. The amplifier according to claim 3 wherein said filament is amonocrystalline iron whisker.

5. A non linear device com-prising a resonant wave guide cavity, inputmeans coupling first and second frequencies of radio frequency energy tosaid cavity at the same time to produce in said cavity andelectromagnetic field distribution corresponding to each of saidenergies including electric field maxima and minima, an elongated memberfor supporting electric conduction and for supporting a magnetic fieldtherealong which member exhibits non-linear magnetization, said memberbeing disposed at a location of high electric field concentration in 1 1said cavity having at 1639i: a major component of its length alignedwith the electric fielddistribution to provide an enhanced radiofrequency magnetic field in said cavity and member, and D.C.magnetization apparatus producing a static magnetic field in said memberfor establishing gyromagnetic resonance therein at one of saidfrequencies, the energy at one of said frequencies being provided at apower lever sufficient to establish a large precessional angle in saidmember as a result of said enhanced radio frequency magnetic fieldcausing substantial non-linear operation whereby to obtain mixingbetween said frequencies.

No references cited.

ROY LAKE, Primary Examiner.

D. R. HOSTETTER, Assistant Examiner.

5. A NON-LINEAR DEVICE COMPRISING A RESONANT WAVE GUIDE CAVITY, INPUTMEANS COUPLING FIRST AND SECOND FREQUENCIES OF RADIO FREQUENCY ENERGY TOSAID CAVITY AT THE SAME TIME TO PRODUCE IN SAID CAVITY ANDELECTROMAGNETIC FIELD DISTRIBUTION CORRESPONDING TO EACH OF SAIDENERGIES INCLUDING ELECTRIC FIELD MAXIMA AND MINIMA, AN ELONGATED MEMBERFOR SUPPORTING ELECTRIC CONDUCTION AND FOR SUPPORTING A MAGNETIC FIELDTHEREALONG WHICH MEMBER EXHIBITS NON-LINEAR MAGNETIZATION, SAID MEMBERBEING DISPOSED AT A LOCATION OF HIGH ELECTRIC FIELD CONCENTRATION INSAID CAVITY HAVING AT LEAST A MAJOR COMPONENT OF ITS LENGTH ALIGNED WITHTHE ELECTRIC FIELD DISTRIBUTION TO PROVIDE AN ENHANCED RADIO FREQUENCYMAGNETIC FIELD IN SAID CAVITY AND MEMBER, AND D.-C. MAGNETIZATIONAPPARATUS